Diesel engines can use particulate filters (PFs) to reduce soot emissions. These filters trap particulate matter that is contained in the exhaust gasses passing through the filter. Periodically, when the filters become full of soot, they are regenerated by raising exhaust gas temperature to the point where the soot is burned. In this way, the filter is again able to retain soot and overall soot emissions are reduced.
Filter regeneration can be controlled based on differential pressure measured across the filter. As more and more soot is stored, a larger differential pressure is measured. See, for example, U.S. Pat. No. 6,405,528, wherein the differential pressure across the filter is determined based on measurements provided by a pair of pressure sensors positioned upstream and downstream of the particulate filter. Once soot accumulation has reached a predetermined level, regeneration of the filter can be initiated. Filter regeneration is accomplished by heating the filter to a temperature that will burn soot particles at a faster rate than the deposition of new soot particles, for example, 400–600° C.
The inventors herein have recognized a disadvantage with the prior art approach. In particular, in order to determine differential pressure across the particulate filter, either two absolute pressure sensors or a differential pressure sensor with two pressure tabs is required to be placed near the filter, which results in high material and installation costs. Further, that the under-body placement of the pressure sensors exposes them to external weather conditions, such as rain, snow, dirt, and cold temperatures, and may therefore degrade their performance. This sensor degradation can result in erroneous pressure measurement, which, in turn, may cause either too frequent, or too infrequent, particulate filter regeneration. Too frequent regeneration (from an erroneously high reading) can result in decreased fuel economy as energy is needlessly spent raising exhaust gas temperatures. Likewise, too infrequent regeneration (from an erroneously low reading) can result in impaired drivability. Further, a degraded sensor output can result in erroneous determinations that the particulate filter itself has become degraded, thereby resulting in unnecessary replacement filter costs.